Predicting the rate of oxygen consumption during the 3-minute constant-rate stair stepping and shuttle tests in people with COPD

The 3-minute constant-rate stair stepping (3-min CRSST) and constant-speed shuttle tests (3-min CSST) were developed and validated for standardized assessment of exertional breathlessness in people with chronic obstructive pulmonary disease (COPD) (1-3). That is, the 3-min CRSST and 3-min CSST require participants to stair-step or shuttle to the pace of an external audio beep, thereby standardizing the exercise stimulus and allowing the breathlessness response to the stimulus to be assessed. The 3-min CRSST and 3-min CSST have good test-retest reliability and are responsive to bronchodilator therapy in people with COPD (1,3,4). The key benefit of these tests over other tests of exertional breathlessness [e.g., cardiopulmonary exercise testing (CPET) on a cycle ergometer or treadmill] is that they are cheap and require limited resources, offering an opportunity for wide-spread use in both clinical and research settings (5). Further, unlike commonly used task-based questionnaires of breathlessness [e.g., Medical Research Council dyspnea scale (MRC) (6)] or self-paced tests of exercise tolerance (6-minute walk test), the 3-min CRSST and 3-min CSST specifically aim to quantify the breathlessness response to a direct and standardized exercise stimulus (2). This overcomes problems when the level of physical activity or walking speed during self-paced exercise tests are adjusted from one evaluation to another according to the level of breathlessness experienced (7). For example, a person with COPD who initiates effective bronchodilator therapy may engage in more physical activity, and thus, experience and report a similar (or even higher) level of breathlessness on a task-based questionnaire or at the end of a self-paced exercise test. In this situation, the benefits of bronchodilation may not be captured using common breathlessness assessment approaches, and true treatment effects may be overlooked. Assessment at a standardized level of exertion is, therefore, key for valid measurement of breathlessness and its response to therapy (5,7,8)